1. Field of the Invention
The present invention relates to a heat exchanger, which is installed in a vehicular air conditioning apparatus that performs temperature adjustment of a vehicle compartment, whereby the heat exchanger is used by the vehicular air conditioning apparatus for heating air that is blown into the vehicle compartment.
2. Description of the Related Art
A vehicular air conditioning apparatus, which is mounted in a vehicle, for example, is equipped with a first blower for drawing in internal and external air with respect to the vehicle into a casing, and a second blower for drawing in air from the vehicle interior into the casing. In this case, for example, air that is introduced from an external air introduction port by rotation of the first blower is heated by a heat exchanger, passes through a first air passage, and is blown toward the front seats in the vehicle compartment from a blow-out port. Together therewith, air that is introduced from an internal air introduction port by rotation of the second blower, after being heated by the heat exchanger, passes through a second air passage and is blown out toward the rear seats.
This type of heat exchanger for use in a vehicular air conditioning apparatus comprises a pair of tanks disposed on upper and lower sides of the heat exchanger, and heat exchanger passages connected between the tanks and through which a medium for carrying out heat exchange flows. A pair of conduits for supplying and discharging the medium with respect to the heat exchanger passages are connected respectively to the tanks.
In addition, for example, utilizing the heat exchanger 1 shown in FIG. 9A, as disclosed in Japanese Laid-Open Patent Publication No. 2003-336991, the medium (e.g., hot water) supplied from one of the conduits positioned on a downward side is supplied into the heat exchanger passage 3 from one of the tanks 2a, and after flowing upwardly therethrough, passes through the other tank 2b positioned on the upper side and is discharged to the exterior from the other conduit. At this time, heat exchange is carried out on the air that passes through the heat exchanger 1, whereupon air that has undergone heat exchange is supplied downstream. Further, with the heat exchanger 4 shown in FIG. 9B, the center of the heat exchanger passage 5 is divided, and conduits are connected respectively to both sides of one of the tanks 6a disposed on a lower portion thereof. A medium (e.g., hot water) supplied to the one tank 6a from one of the conduits disposed on the righthand side rises upwardly in the interior of a heat exchanger passage toward the side of the other tank 6b. At the tank 6b, after having flowed therethrough in a leftward direction, the medium passes by the lefthand side of the divided heat exchanger passage 5 and proceeds to flow downward, and after passing again through the first tank 6a, the medium is discharged through the other conduit disposed on the lefthand side.
The above-described heat exchanger is applied to a vehicular air conditioning apparatus equipped with two first and second blowers, which are capable of blowing air independently to the front and rear seats in the vehicle compartment. In this case, it is conceived that the heat exchanger is disposed so as to straddle between a first air passage and a second air passage, whereby the air that flows through the first and second air passages can be adjusted in temperature independently.
However, with this type of vehicular air conditioning apparatus, for example, in the event that external air (air) is taken in by the first blower in an environment where the outside air temperature is low, when such air is heated by the heat exchanger via the first air passage, the hot water, which serves as the heat exchange medium, is cooled by the low temperature external air. Because a structure exists in which the hot water, which has been lowered in temperature, is circulated through the heat exchanger and flows through the region over which air supplied from the second air passage passes, the air supplied from the second blower cannot be heated to a predetermined temperature by the hot water medium, which has been cooled. More specifically, air that flows through the second air passage is influenced by the low temperature air (external air) that is introduced through the first air passage, and such air cannot be heated to a predetermined temperature. Since the temperature of air that passes through the second air passage and is blown toward the rear seats inside the vehicle compartment is lowered, there is a concern that the comfort of passengers in the vehicle will be adversely affected.